Re: [PATCH 0/3] btrfs-progs: remove full /dev scanning

[Chris Mason <clm@fb.com>]

On 08/26/2014 10:51 AM, Eric Sandeen wrote:
> On 8/26/14, 5:55 AM, David Sterba wrote:
>> On Thu, Aug 21, 2014 at 08:08:57PM +0200, Goffredo Baroncelli wrote:
>>> Of course I (we) don't care cdrom and/or floppy, but this raises 
>>> the question: are there other block devices which aren't showed in 
>>> proc/partitions ? 
>>
>> cdrom appears as /dev/sr0, floppy is /dev/fd0 if the respective modules
>> are loaded, no breakage here.
>>
>>> I am thinking to some less common hardware like
>>> NON USB sd disk (I saw this kind of hardware, but now I don't have 
>>> it in my hands....).
>>
>> A block device whose driver calls register_blkdev should appear in
>> proc/partitions, if not then I think it's a bug or a very non-standard
>> interface.
>>
>> I don't know about any other cases where full /dev scan would reveal
>> something that /proc/partitions not, so I guess it's safe to remove it.
> 
> Yesterday, Chris did mention <something something mumble> about /dev/mapper/*
> 
> [12:57]  <cmason> I got inconsistent results from /proc/partitions
> [12:57]  <cmason> this was 3 years ago now
> [12:58]  <cmason> it didn't find everything for dm devices, yeah
> [12:58]  <cmason> especially dm multipath got really confused
> 
> and I'll be honest, I didn't test with devicemapper devices, much
> less dm multipath, so I suppose that's warranted prior to removal.
> 
> I'll see what I can do.
> 
> If there's a problem, I bet there's a solution that doesn't involve
> scanning everything under /dev ...

That's definitely the problem I hit, but it was years ago.  I'm willing
to bet we're safe to keep /proc/partitions now.

-chris